The overall goal of this proposal is to understand how the serine/threonine protein kinase Akt cooperates with other oncogenic/tumor survival pathways to cause breast cancer, and to develop preclinically and clinically novel combination therapies for more effective breast cancer treatment. Overexpression of receptor tyrosine kinases such as ErbB2, which leads to persistent hyperactivation of a large number of oncogenic/tumor survival proteins such as Ras, Rho, Ral, Akt, MEK and STAT3, is associated with poor prognosis, resistance to chemotherapy and shortened survival time of breast cancer patients. This prompted the development of novel agents such as the ErbB2 antibody Herceptin and small molecule inhibitors of the activation of Akt (Triciribine (TCN/TCN-P)), MEK (CI-1040), Ras and other farnesylated proteins (Tipifarnib) and Rho and other geranylgeranylated proteins (GGTI-2417). A large body of evidence implicates Akt in cancer development and maintenance, but interfering with Akt alone does not appear to be sufficient, suggesting that blocking other pathways in combination with Akt inactivation is critical to thwarting breast cancer. For example, inactivation of Akt with TCN in combination with either Tipifarnib or GGTI-2417 is synergistic, suggesting that Akt cooperates with farnesylated and geranylgeranylated (prenylated) proteins yet to be identified, to cause breast cancer. In this application we propose to use high throughput screens based on RNA interference to identify these prenylated proteins and to develop novel combination therapies for breast cancer. The hypothesis to be tested is that hyperactivated Akt cooperates with prenylated proteins to contribute to breast oncogenesis and tumor resistance, and that targeted intervention of Akt in combination with other anti-signaling and cytotoxic agents suppresses tumor growth and induces apoptosis in breast tumors. The specific aims are: 1) To identify prenylated proteins whose knockdown sensitizes breast cancer cells to inactivation of Akt by TCN, 2) To identify specific prenylated proteins whose knockdown sensitizes breast cancer cells to the knock down of the three Akt isoforms, Akt1, Akt2 or Akt3, 3) To determine if inactivation of Akt by TCN sensitizes human breast tumors to cytotoxic and anti-signaling agents relevant to breast cancer treatment and, 4) To conduct hypothesis-driven phase I/II clinical trials of pre-operative TCN-P plus weekly paclitaxel and Tipifarnib followed by AC plus Tipifarnib in patients with locally advanced and metastatic breast cancer. Results from these studies will lead to the identification of oncogenic/tumor survival prenylated proteins that cooperate with Akt to cause breast cancer as well as to the design of novel combination therapies that will improve breast cancer survival by increasing the cure rate in patients with locally advanced breast cancer.